1. Field of the Invention
The invention relates to a metal member having precious metal plating and a manufacturing method thereof. More specifically, the invention relates to a metal member having a precious metal plating which does not peel away easily and a manufacturing method thereof.
2. Description of the Related Art
When forming a separator of a fuel cell using material in which the contact resistance between the fuel cell and the electrode increases when used as it is, precious metal plating is applied to the portion of the separator surface that contacts the electrode. For example, in Japanese Patent Application Publication No. JP-A-2001-6713, stainless steel with a precious metal adhered to its surface is produced by performing a process in which minute amounts of platinum are deposited on the surface of stainless steel while mechanically removing a passive film (oxide film) by lightly polishing the stainless steel with silicon carbide paper.
Further, in Japanese Patent Application Publication No. JP-A-2000-164228, a fuel cell separator includes a coating layer which has a multiple layered structure formed of two layers or more of a low electrical resistant layer, a corrosion resistant layer and peeling resistant layer. Japanese Patent Application Publication No. JP-A-2000-323151 describes a fuel cell including a separator in which a conductive contact point having corrosion resistance is arranged at a part of conductive gas passage plate abutting on a gas diffusion electrode. Japanese Patent Application Publication No. JP-A-2002-134136 provides a surface treatment method in which a coating particles are vibrated and made to flow by supersonic beam; and while the surface oxide film of the passive state metal is removed by the collision of the coating particles against the surface under treatment, the coating particles are attached to part or whole of the oxide film removed part.
However, even if the precious metal plating layer is firmly bonded to the other metal of the member immediately after the precious metal layer is formed, as time passes a metal compound layer forms at the boundary surface of the plating layer and the other metal, and as a result, the precious metal plating layer may peels away. This kind of problem is not only limited to separators of fuel cells, but can occur whenever a metal member in which an oxide film tends to form on the surface has been plated with precious metal.